Solution
In a host PC, BIOS or UEFI are the firmware interfaces that initialize hardware components and boot an operating system. They are responsible for reserving a fixed number of PCI/PCIe resources (bus number and memory) for Thunderbolt.
Whenever a device is connected to a Thunderbolt port, it takes up resources from the Thunderbolt-preserved resource. The preserved resource is crucial for handling hot-plug events and dynamic device management. If you connect a resource-hungry device (e.g., USB to 8-port RS232 converter), it could take up most of the resource from the Thunderbolt-preserved resource pool. This might cause the other Thunderbolt-connected NI PXI or PXIe system not to get enough PCI resources, and thus malfunction.
To resolve the issue, you might try to increase the amount of memory reserved for the Thunderbolt in BIOS. Note that this option might be hidden by the PC vendor; thus, you need to get the PC vendor's assistance to unhide the configuration. There might be a chance that the PC does not have this configuration. If the host PC does not have the option to change the pre-allocated memory resources, please consider changing to a different model or a different brand of host PC. Using back the same model of host PC would not solve the issue.